AQA A Level Chemistry复习笔记3.1.2 Types of Formulae

Types of Formulae


  • The general formula is a formula that represents a homologous series of compounds using letters and numbers
    • Eg. the general formula of alkanes is CnH2n+2
    • A homologous series is a group of organic compounds that have the same functional group, the same general formula and the same chemical properties


  • The structural formula is a formula that shows how the atoms are bonded to each carbon atom in a molecule
  • The displayed formula is a 2D representation of an organic molecule showing all its atoms (by their symbols) and their bonds (by single, double or triple bonds)
  • The skeletal formula is a simplified displayed formula with all the carbon and hydrogen (C-H) bonds removed

Overview of the Formulae of Organic Compounds Table



Worked Example

Drawing skeletal formulae of molecules

Draw the skeletal formula of the following molecules:

  1. CH3(CH2)3OH
  2. (CH3)2CHCH2OH
  3. CH3CH2OCH2CH3




Worked Example

Drawing displayed formulae of molecules

Draw the displayed formula of the following molecules:Copy-of-WE-An-Introduction-to-AS-Level-Organic-Chemistry-Drawing-displayed-formulae-of-molecules_1





Molecular & Empirical Formulae

  • The molecular formula shows the number and type of each atom in a molecule
    • Eg. the molecular formula of ethanoic acid is C2H4O2


  • The empirical formula shows the simplest whole number ratio of the elements present in one molecule of the compound
    • Eg. the empirical formula of ethanoic acid is CH2O


Worked Example

Deducing molecular & empirical formulaeDeduce the molecular and empirical formula of the following compounds:Copy-of-WE-Deducing-molecular-empirical-formulae_1